Recovery of carboxylic acids



Patented Mar. 24, 1942 2,-z77,31s v RECOVERY OF CARBOXYLIC ACIDS Lionel S. Galstaun, San Francisco, Calif., assignor to Tide Water Associated Oil Company, San Francisco, Calii., a corporation of Delaware No Drawing. Application July 13, 1940,

Serial No. 345,375 I 14 Claims. (cacao-514i This invention relates to the separation and recovery of organic acids from aqueous alkali solutions containing alkali salts of both the carboxylic and phenolic types. The invention particularly adapted to the recovery of carboxyhc acids from petroleum refinery spent alkali liquors obtained from the neutralization of raw straight-run gasoline and kerosene distillates. Concentrations of organic acidic bodies up to 15% or by volume may be found in such spent alkali solutions, the actual concentration in any given case depending on the initial concentration of alkali and the extent to which the solution has been used, or spent." Of these acidic bodies, organic acids of the carboxylic type (naphthenic acids in the case oi. distillates from California crude petroleum) generally account for 20 to 50 percent, the remaining 80 to 50 percent being bodies of weaker acidic nature, principally of the phenolic type (i. e., having an OH group directly attached to an aromatic nucleus) which, for convenience,will be hereinafter designated as ,phenols. The spent alkali liquors will, in addition, generally contain inorganic sulphides and polysulphides as well as a minor amount of hydrocarbon matter.

Likewise, the invention is adapted to the recovery of carboxylic acids fromspent alkali obtained from the neutralization of cracked petroleum distillates. In this case the carboxylic acids are principally aliphatic acids of the saturated and unsaturated series. Phenols are present as in the case of spent alkali from straight run distillates. In addition mercaptans may be present to a greater or less extent depending, among other things, on the type ofcracking stock and the conditions under which the distillates are treated with alkali.

Various uses have been found in the arts for naphthenic and other carboxylic acids as well as for the phenols. Naphthenic acids, particularly the lower members of the series, are extensively employed in the paint, textile, and petroleum industries. Fatty acids are in general use in the chemical industries. Such uses gen erally require that the acids be relatively free from phenols and other impurities.

It is therefore an object of the invention to recover carboxylic acids from solutions containing alkali salts of both the carboxylic and phenolic types.

Another object is the recovery of naphthenic acids from petroleum refinery spent alkali liquors containing salts of naphthenic acids and phenols.

uors containing salts of aliphatic acids and phenols. 4

Other objects will be apparent from the following description.

In the recovery of naphthenic acids from petroleum spent alkali solutions it is common practice to neutralize the solution with sulphuric (or hydrochloric) acid. This neutralization eiTects a separation -of all the organic acids from the' aqueous solution as an oily layer which may be recovered by decantation. This method is non-selective as to the type of acidic bodies recovered and, when naphthenic acids and phenols are both present as salts in the alkali solutions, the oily layer will comprise both types of acids. Also, when sulphides are present, free sulphur may be precipitated from the aqueous layer and dissolve in the oily layer.

When a separation of the phenols from the naphthenic acids is required, it is customary to treat the oily layer 'with'alkali to effect a partial neutralization. The step in general involves adding sufiicient soda to the oily layer to form the soda soaps of the naphthenic acids but not of the phenols. The exact amount of caustic soda required for this pu pose may be determined stoichiometrically if the composition of the oily layer is known. Alternately, hydrogen ion control may be employed and caustic soda added until a pH value of 9 or 10 is obtained. The

mixture of sodium naphthenates and free phenols may then be separated into the phenols and naphthenates. This may be by steam distillation in which only the volatile free phenols are distilled, or the separation may be accomplished by extraction with water and other solvents. This partial neutralization step has the disadvantage of requiring extreme care in adding the required amount of caustic soda. Also, the caustic soda so added represents an economic loss.

According to the present invention no additional caustic soda is required beyond that in the original spent alkali, free sulphur is not released naphthenic acids and phenols, and the mixture of naphthenates and free phenols is obtained in one step without the necessity to contaminate the of careful control of reagent quantities.

To this end a spent alkali spent alkali from lates) is neutralized with sulphur dioxide'gas. The point of proper neutralization is easily obtained as it is satisfactory merely to saturate the solution containing phenolates and naphthenates (in the .case o f treating straight-run dis til-:,

spent alkali solution with sulphur dioxide at about atmospheric pressure in order to obtain satisfactory neutralization. At this point an oily layer separates from the aqueous solution. The oily layer will be found to contain free phenols and sodium naphthenates, whereas the aqueous layer will be found to be substantially free of both naphthenates and phenols.

The oily layer, containing naphthenates and free phenols, is then separated from the aqueous phase and processed to-separate the free phenols from the naphthenates. Due to the greater solubility of sodium naphthenate in water, the naphthenates may be recovered from the mixture by extraction with water, or by simultaneous extraction with two immiscible solvents such as petroleum naphtha and water, the naphtha absorbing the phenols and the water the naphthenates.

The preferred method of separating the free phenols from the naphthenates depends on the fact that the free phenols have a. far greater volatility than the sodium (or other) salts of the naphthenic acids. Consequently, the desired separation may be made readily by distillation, either with fire or with steam as is desired. Vacuum distillation may, at times, be used to advantage. The distillation is carried to the point at which there is a considerable rise in temperature, indicating that only the naphthenates remain in the still. During this distillation some of the higher molecular weight naphthenates may hydrolyse and the resulting naphthenic acids may be carried over into the distillate with the phenols. The removal of these high molecular weight acids from the mass of naphthenic acids is generally a desirable feature resulting in an ultimate naphthenic acid product of higher acidity. Suitable continuous distillation may be substituted for batch distillation if desired, such substitution being within the skill of a distillation engineer.

If itis required to recover free naphthenic acids instead of naphthenates, the naphthenate residue from the distillation (or the water phase from the water extraction) is treated with a mineral acid, such as sulphuric acid, to decompose the sodium soaps and cause a separation of the free acids.

An alternative procedure, specifically applicable to naphthenic acids, which largely eliminates the necessity of neutralizing with sulphuric acid, is based on the fact that naphthenate soaps hydrolyse to a considerable extent if the temperature is 'sufliciently high. According to this alternate procedure, after the free phenols have been removed by distillation, the temperature of the still is raised either by the application of pressure or by concentrating the solution in the still by distilling oil water. At the increased temperature, above about 400 F., the naphthenate soaps dissociate yielding free naphthenic acids and free alkali. The released naphthenic acids may then be readily distilled. Obviously, some water (or steam) must be present to effect the hydrolysis.

In applying the invention to spent alkali obtained in the neutralization of cracked petroleum distillates, the same procedure is followed. In this case, however, the carboxylic acids are principally aliphatic acids of the saturated and unsaturated series. Phenols are present, as in the case of spent alkali from straight run distillates, and separation of the phenols from the carboxylic acids is accomplished in the same manner.

Unless special precautions are taken in the treatment of pressure distillates, the spent alkali will generally contain mercaptides in addition to aliphatic acids and phenols. These mercaptides will be converted into mercaptans by the treatment with sulphur dioxide. The mercaptans will then-be subsequently found in the phenol portion after the separation of the aliphatic acids from the phenols. Consequently, in order to recover phenols free from mercaptans, the mercaptans should first be removed from the spent alkali by steam stripping, or other distillation. Alternately, by special methods of treating the cracked distillates, spent alkali, solutions relatively free from mercaptans can be obtained. A preferred alkali solution for use in the invention is that obtained from the first or hot caustic stage of the two-stage method of treating pressure distillate described in U. S. Patent Number 2,183,968 issued to McCormick and Lazar. This spent caustic solution is relatively free from mercaptans.

The organic acids obtained by application of this invention to spent caustic from pressure distillate treating can be resolved into pure components by fractional distillation. Considerable amounts of butyric, isobutyric and higher homologues may be obtained from this source. Of these, isobutyric acid is of importance in the petroleum industry.

The invention may be more readily understood from the following examples.

EXAMPLE .I

- Forty gallons of spent caustic soda solution derived from the treatment of raw California gasoline distillate were treated with sulphur dioxide gas by passing the gas into the solution. Analysis of solution before treatment with sulphur dioxide showed that it contained 55.2 grams per liter of free sodium hydroxide.

After about two hours of the SO: treatment it was noted that oily matter was beginning to separate, The bubbling was continued for an additional half hour and a sample of the oily matter removed for analysis. The results of this analysis are given in Table I.

Table I Naphthenic acids percent 22.6 Equivalent weight of naphthenic acids 306 The treatment with S0; was continued for four hours more. At this time the aqueous phase reacted neutral to litmus. The S02 bubbling was continued for an additional hour, making the total treating time 7 hours. The yield of oily matter was 6 gallons or 15.6 percent by volume. Analysis of the oily matter is given in Table II.

Table II Naphthenic acids percent 376 Equivalent weight 309 Ash (as sulphate) percent 6.6 Water by distillation do 12 Treatment with sulphuric acid of the aqueous phase remaining after removal of the oily matter showed that substantially no organic acids remained therein.

The oily matter obtained from the S02 treatment was subjected to distillation with superheated steam. The still was heated suiilciently to prevent substantial condensation of steam. The first portion of overhead product (water and phenols) was allowed to settle and the "phenol layer separated and dried over anhydrous calcium chloride. The yield of dry product was 40% of the charge. Analysis of this product is given in Table III.

Table III Naphthenic acids percent 4.6 Equivalent weight of naphthenic acids- 1154 The second portion of overhead product was treated in the same manner. The yield was 20% and the analysis is given in Table IV.

Table IV.

Naphthenic acids percent 27.8 Equivalent weight of naphthenic acids 816 moved from the still (accompanied by rise in its temperature) the ratio of oily product to water in the condensate increased slowly at first then very abruptly, and .finally dropped just as abruptly to substantially zero. Atthis point the still was found to contain a substantially dry, solid residue. Incipient decomposition with smoking was noted and the heating was stopped. The sudden rise in the ratio of oily product to water in the condensate indicated that the still contents had reached the dissociation temperature of the sodium naphthenate. The analysis of the dried oily overhead product (yield 22%) is shown in Table V.

Table V Naphthenlc acids per cent 98.1 Equivalent weight of naphthenic acids-- 277.6

Table VI is a compilation of the data given in Tables III to V.

Table VI Equivalent weight oi naphthenic acids Volume (percent oi charge) Na hthenic ac ds, percent Fraction number naphthenic acids to distill are the heaviest members. This occurs because the heavy members are the weakest acids and hence are the first to dissociate as the temperature is raised.

If higher purity than 98% is desired, the 98% acids may be treated with the stoichiometric quantity of caustic soda to form the soda soaps and then redistilled at relatively low temperature to strip 011 the impurities. The temperature may then be raised to distill oil free naphthenic acids, or the soaps may be decomposed with sulphuric acid to recover the free naphthenic acids. It should be noted, however, that 98% naphthenic acids represent a sufllcient purity for the majority of industrial applications.

Exmrn II 1800 cc. of spent caustic soda solution derived from the hot caustic treat disclosed in the above mentioned U. 8. Patent 2,133,968 was saturated with sulphur dioxide. The volume of the oily layer obtained was 250 cc. or 13.9 percent by volume.

The oily layer was steam distilled and 160 cc. obtained as a steam distillate. The residue was a viscous mass which could not be distilled. Butyric acid was identified in this residue. The overhead portion was principally phenolic in composition. It is clear that except for the fact that the sodium salts of the aliphatic acids cannot be dissociated by heat without decomposition the processing procedure of spent caustic from treating straight run and cracked petroleum fractions is substantially the same.

In the foregoing the invention was illustrated I as applied to the recovery of (a) naphthenic acids from spent alkali derived from the treatment v of straight run petroleum distillates and. (b) allphatic acids from spent alkali derived from the treatment of cracked petroleum distillates. The invention in its broadest scope is applicable to the recovery of strong carboxylic acids from alkali solutions containing carboxylic soaps and weakly acidic phenolic compounds, regardless of the source of such solutions.

I claim:

1. The process of recovering organic acids from alkali solutions containing salts of the same which comprises: neutralizing with sulphur dioxide an aqueous alkali solution containing alkali metal salts of carboxylic acids and alkali metal salts of phenols whereby there is formed an aqueous layer and an oily layer containing free phenols and carboxylic acid salts, separating the 'oily layer from the aqueous layer, separating carboxylic acid salts from the oily layer,

and recovering carboxylic acids from said carboxylic acid salts.

2. The process of recovering carboxylic acid salts from alkali solutions containing the same which comprises: neutralizing with sulphur dioxide an aqueous alkali solution containing alkali metal salts of carboxylic acids and alkali metal salts of phenols whereby there is formed an aqueous layer and an oily layer containing free phenols and carboxylic acid salts, separating the oily layer from the aqueous layer, and separating carboxylic acid salts from the oily layer. I

3. The process of recovering carboxylic acid salts from alkali solutions containing the same which comprises: neutralizing with sulphur dioxide an aqueous alkali solution containing alkali metal salts of carboxylic acids andalkali metal salts of phenols whereby there is formed an aqueous layer and an oily layer containing free phenols and carboxylic acid salts, separating the oily layer from the aqueous layer, and distilling said oily layer to remove therefrom said phenols.

4. The process of recovering carboxylic acid salts from alkali solutions containing the same which comprises: neutralizing with sulphur dioxide an aqueous alkali solution containing alkali metal salts of carboxylic acids and alkali metal salts of phenols whereby there is formed an aqueous layer and an oily layer containing free phenols and carboxylic acid salts, separating the oily layer from the aqueous layer, and extracting carboxylic acid salts from said oily layer with water.

5. The process of recovering organic acids from comprises: neutralizing with sulphur dioxide an aqueous alkali solution containing alkali metal salts of carboxylic acids and alkali metal salts of phenols whereby there is formed an aqueous layer and an oily layer containing free phenols and carboxylic acid salts, separating the oily layer from the aqueous layer, extracting carboxylic acid salts from said oily layer with water, and neutralizing the water extract with a mineral acid to liberate carboxylic acids.

'I. In a process of recovering organic acids from alkali solutions containing salts of the same the step which comprises: neutralizing with sulphur dioxide an aqueous alkali solution containing alkali metal salts of carboxylic acids and alkali metal salts of phenols.

8. In a process of recovering organic acids from alkali solutions containing salts of the same the combination of steps which comprises: neutralizing with sulphur dioxide an aqueous alkali solution containing alkali metal salts of carboxylic acids and alkali metal salts of phenols whereby there is formed an aqueous layer and an oily layer containing free phenols and carboxylic acid salts and separating the oily layer from the aqueous layer.

9. The method of recovering naphthenic acids from spent alkali solutions which comprises: adding sulphur dioxide to a spent aqueous alkali solution derived from the treatment of a light straight run petroleum distillate and containing alkali metal naphthenates and phenolates to cause the separation therefrom 01' a layer containing free phenols and akali metal naphthenates, separating said layer from said solution, separating naphthenates from said layer, and recovering naphthenic acids from the separated naphthenates.

aa'msrs taining free phenols and alkali metal naphtenates, separating said layer from said solution,

distilling said layer to remove therefrom said phenols, and neutralizing the remaining naphthenates with a mineral acid.

11. The method of recovering naphthenic acids from spent alkali solutions which comprises: adding sulphur dioxide to a spent aqueous alkali solution derived from the treatment of a light straight run petroleum distillate and containing alkali metal naphthenates and phenolates to cause the separation therefrom of a layer con-l taining free phenols and alkali metal naphthenates, separating said layer from said solution, distilling said phenols from said layer, heating the remaining naphthenates in the presence of steam to a temperature at which the naphthenates hydrolyse, and distilling the resulting naphthenic acids.

12. The method of recovering naphthenic acids from alkali solutions which comprises: adding sulphur dioxide to an aqueous alkali solution containing alkali metal naphthenates and phenolates to cause the separation therefrom of a layer containing free phenols and alkali metal naphthenates, separating said layer from said solution, distilling said phenols from said layer, heating the remaining naphthenates in the presence of steam to a temperature at which the naphthenates hydrolyse, and distilling oil? the resulting naphthenic acids.

13. The method of recovering aliphatic acids from spent aqueous alkali solution which comprises: adding sulphur dioxide to a spent aqueous alkali solution derived from the treatment of a light cracked petroleum distillate and containing alkali metal salts of aliphatic acids and of phenols to cause the separation therefrom voi! a layer containing free phenols and alkali metal salts of aliphatic acids, separating said layer from said solution, separating aliphatic acid salts from said layer. and recovering aliphatic acids from the seiiagrated salts by neutralization with a mineral ac 14. The method of recovering aliphatic acids from spent alkali solutions which comprises: adding sulphur dioxide to a spent aqueous alkali solution derived from the treatment of a light cracked petroleum distillate and containing alkali metal salts of aliphatic acids and of phenols to cause the separation therefrom of a layer containing free phenols and alkali metal salts of aliphatic acids, separating said layer from said solution, distilling said layer to remove therefrom said phenols and neutralizing the remaining aliphatic acid salts with a mineral acid.

LIONEL S. GALSTAUN. 

